1. Field of the Invention
The present invention relates to a foothold comprising a tread, side portions positioned at both sides of the tread and legs to be inserted into a concrete wall.
2. Background of the Invention
A conventional foothold including a tread, side portions positioned at both sides of the tread and legs to be inserted into a concrete wall is disclosed in Japanese Patent Laid-Open Publication 10-292412, which foothold includes spherical bodies integrally formed with the side portions at boundaries between the side portions and legs, and collar pieces fitted to the curved wall (such as a manhole inner wall) are slidably provided on the spherical bodies, wherein the collar pieces are pressed against the wall surface.
In the conventional foothold, if the diameters of the spherical bodies in which the collar pieces fitted to the curved wall such as the manhole inner wall are small, the collar pieces easily come out from the spherical bodies and hence the collar pieces can not be reliably retained relative to the spherical bodies, leading to a drawback that the foothold can not be reliably held relative to the manhole inner wall. On the other hand, if the diameters of the spherical bodies are large, the collar pieces are slidable relative to the spherical bodies, leading to a drawback that the collar pieces are also made large like the spherical bodies, and the tip ends of the spherical bodies are brought into contact with the manhole inner wall when the foothold is fixed to the inner wall. To avoid such drawbacks, the spherical bodies are provided such that they protrude a large amount from the side portions of the foothold, thereby making the entire foothold large.